International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 3

Number 3

September 2009

315

1 INTRODUCTION

The submitted contribution provides one of the pos-

sible approaches of evaluating the impact of building

windmills (WE) in a given location exerted on the

operational parameters of the radio-location system

(RLS). For the reason of providing the required cov-

erage the RLS is protected by a protective zone of

determined by the distances and height of plains of

the protection zone band. If, in the protection zone,

there are any obstacles which overlap with the de-

termined planes, then deformation of the RLS cov-

erage in the vertical plane may occur resulting in the

loss of radar signal on flying objects.

2 LOSS OF RADIO-LOCATION SIGNALS

RESULTING FROM SHADOWING

The importance and acuteness of the mechanism of

any impact will depend on the designation of RLS

and its operating environment. Among the most im-

portant influences of Windmill exerted on the RLS

is the loss of signals as a result of shadowing.

The technical data imply the WE has a great

cross-section area. In case when locating the WE in

the vicinity of the RLS results in late in its shadow-

ing. This is when the radiolocation shadow is gener-

ated in the vicinity of the RLS, see Figure 1. The

dimension of such areas depend on the size and mu-

tual distances between the WE, their number, dis-

tances from the RLS and the surrounding terrain.

If the height of the obstacle at small distances be-

hind the WE exceeds the height of the WE, then the

influence of the WE exerted on the reduction of the

direct line-of–sight is to be neglected. If the altitude

(height above see level) of the obstacle located be-

fore the WE exceeds the height of the WE, than the

WE has no effect on the direct lined-of-sight of the

RLS, which is entirely determined by the dimen-

sions of the obstacle.

The implications of the shadowing can be quite

successfully prognosed applying the methods of

modeling and simulation. At performing modeling

and simulation of the signal loss resulting form

shadowing, a special software can be used which is

capable of simulating the direct line-of-sight be-

tween the RLS antenna and the planned WE. Ad-

vantages may result from the use of such software

which enable access into the digital model of terrain

and thereby modeling obstacles in it.

Figure 1. Mechanism of shadowing

The Impact of Windmills on the Operation of

Radar Systems

M. Dzunda, V. Humenansky, D. Draxler, Z. Csefalvay & P. Bajusz

Faculty of Aeronautics, TU of Kosice, Slovakia

ABSTRACT: The contribution provides solutions to the impact of planned building of windmills exerted on

the operation of radar equipment. The major negative factors involved have been determined and considered

as to how the planned building of wind power stations influences the operation of radar systems developing a

procedure of evaluating their effects.

316

The results from the simulation will reveal which

windmills cause loss of radiolocation signals result-

ing from shadowing, thereby discarding them from

the construction plan. The success criterion is the

minimally acceptable shadowing that must not be

present in the areas of interest.

The influence of shadowing of a WE exerted on

the RLS is presented in Fig. 2.

Figure 2. Shadowing of radar signals

3 MEASURED RADIO-LOCATION SIGNALS

AS REFLECTIONS FROM WINDMILLS

Everywhere, where, the RLS is used for local air-

ports, and Terminal control areas (TMA), the reflec-

tions from the WE are of the highest importance. It

is due to the fact that such reflections may divert the

controller´s attention and make it difficult for him to

monitor further data displayed in the same place on

the monitor (Klima trough Bálint). Such an image

may also lead to the generation of false tracks of the

target which may develop into a more acute problem

for air traffic controller. The reflection may cover

the targets and the radio-location information on the

screen directly over or in the close vicinity of

a windmill complex an in some cases may cause the

loss of reflections of aircraft.

WE, as specified in the basic technical data sec-

tion, has a great area of the stand, which is manufac-

tured from conducting material reflecting electro-

magnetic waves striking it. The non-moving WE

stands can be considered for a non-moving (fixed)

target. Modern radiolocation systems are equipped

with circuits for jamming fixed targets, so we as-

sume that jamming the reflections and WE stands

will no longer pose problems, provided that the RLS

is operating in the mode of fixed targets suppression.

The mechanism of RLS signals is presented in

Fig. 3. The precondition of generating such reflec-

tions is the sufficient amount of reflected signals, re-

ceived by the receiver antenna.

Figure 3. Mechanism of how reflections are generated

We suppose that false targets may result from the

reflections from WE which are in direct line-of-sight

of the radar. The fact that the WE is situated in the

vicinity of the RLS is another precondition.

More complex problems arise in cases when the

measured signals are reflected from the propeller

blades, which, in line with the technical specifica-

tions, are designed to have a big area and built form

conducting materials reflecting measured radioloca-

tion signals. Under certain conditions, the signals re-

flected form the propeller blades may be evaluated

by the RLS as moving targets.

This rate is to be probably changed along the en-

tire length of the RLS. One of the ways of determin-

ing the maximum way of acceptable reflection is the

use of so called protection maps.

At such a simplified map, the scales of reflections

are seen in Fig. 4.

Figure 4. Reflections from windmills

When evaluating the reflections, we will proceed

from the equation:

( )

GvGP

odr

σλ

(1)

317

where L are losses occurring at propagation of the

electromagnetic energy in the environment, G

is the

gain on receipt, G

is the gain in transmission, λ –

wavelength, R – distance between the WE and the

RLS, σ the effective radar cross-section from which

the signal was reflected and P

is the transmitter per-

formance. The success criterion is termed as the

minimum tolerable rate of reflections from the WE

per square km in an hour.

4 CONCLUSION

The operation of RLS is negatively influenced by

four main factors. Among them are the mistakes in

measuring the target azimuth, generation of false

targets, loss of signal due to shadowing and degrada-

tion of signal as a result of multi-way propagation.

When evaluating all the four factors, the key param-

eter is assigned to the terrain cross section on the

connecting line between the WE-RLS and the dis-

tance between the wind mill and the radiolocation

system. If there is no direct line-of-sight between

them, with the distances increasing between them,

the effects of building the WE on the RLS are sub-

stantially decreasing.

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